Lipase (triacylglycerol acylhydrolase, EC3.1.1.3) is an enzyme that catalyzes the hydrolysis of triglycerides into fatty acids and glycerides or glycerols and performs an essential role as one of the three digestive enzymes, together with amylase and protease, which digest foods. Lipases are naturally sourced from a broad range of organisms including animals, plants and microbes.
In addition to playing important roles in lipid metabolism in vivo, lipases are useful for enhancing the flavor of cheese, increasing free fatty acids upon vegetable fermentation, deepening the flavor upon meat fermentation, and lipolyzing fish. Further, the use of lipases has now extended to the synthesis of expensive, optically pure isomers. Moreover, lipases find application in a variety of industries. As some examples thereof, the applications of lipases in the dairy industry include making cheese via the hydrolysis of milk fats and the lysis of butterfat or cream. In the detergent industry, lipases can be used to prepare laundry detergents or washing machine detergents. The enzymes can reduce the environmental load of detergent products since they save energy by enabling a lower wash temperature to be used. The scope of application of lipases in the oleochemical industry is enormous, including the manufacture of unsaturated fatty acids and soaps and the production of cocoa butter from cheap palm oil. In the paper manufacturing industry, lipases are utilized to remove resins or rosins from woods and ink from waste paper. Turning to the pharmaceutical industry, the use of lipases includes the synthesis of separate R- and S-optical isomers, the separation of racemates and the manufacture of drugs. The cosmetic industry applies lipases to the production of skin cosmetics including waxes, suntan creams, and bath products. Also, lipases are useful in the energy industry as a means for producing biodiesel from vegetable oil.
Currently, biodiesel, emerging as new renewable energy, has been produced using chemical catalyst-based methods throughout the world. However, their commercialization has not yet been successful because of the use of a large amount of organic solvents, the high expense of environmental disposal, and high energy consumption attributed to high reaction temperature. For these reasons, intensive attention is paid to processes employing lipase as a catalyst. These processes enjoy the advantage of saving energy thanks to low reaction temperatures, reducing the production cost by creating profits from the by-product glycerol, and being almost free of environmental pollution. However, the enzyme is poor in terms of stability and efficiency vs. cost. The immobilization of the enzyme has been suggested as a way to overcome the drawbacks, but remains distant as a solution to the problem of how to improve enzyme properties. Thus, active research is being done to improve the industrial utility of the enzyme by increasing its enzymatic activity.
Rather than the development of inexpensive and potent lipases, for example, indirect alternatives, such as modified reaction conditions for lipases and enzyme immobilization, have been used to solve the problems associated with lipases. Alternatively, searching for new lipases using metagenomics has been done, but has had no noteworthy achievements. In order to improve the activity of lipases and their substrate specificity, thermal resistance and stability, extensive studies have been done into which the X-ray crystallographic data of various lipases have been collected and the lipases have been modified in such a manner that amino acid residues of the active site and the surrounding area are substituted using protein engineering techniques such as site-directed mutagenesis. Although this brings about an improvement in the activity of lipases, the improvement is only partial.